Method and apparatus for a reflective spatial light modulator with a flexible pedestal

ABSTRACT

An electromechanical system comprising a substrate including a surface region and a flexible member coupled at a first end to the surface region. The system further comprises a base region within a first portion of the flexible member and a tip region within a second portion of the flexible member. The system also comprises a reflective member coupled to the flexible member, including a reflective surface and a backside region, the backside region being coupled to the second end of the flexible member, the reflective surface being substantially parallel to the surface region while the reflective member is in a first state and being substantially non-parallel to the surface region while the reflective member is in a second state, whereupon the flexible member moves from a first position characterized by the first state to a second position characterized by the second state.

BACKGROUND OF THE INVENTION

This present invention relates generally to manufacturing objects. Moreparticularly, the invention provides a method and apparatus forfabricating and operating electromechanical systems. Merely by way ofexample, the invention has been applied to a high fill factormicro-electromechanical mirror array with a hidden, flexible supportpedestal. The method and apparatus can be applied to otherelectromechanical technology as well, including actuators and sensors.

Micro-electromechanical systems (MEMS) are used in a number ofapplication areas. For example, MEMS have been used in micro-mirrorarrays, sensors, and actuators. In some of these applications, asuspended member is supported by a flexible hinge attached to astationary portion of the mirco-mirror array. Flexibly attached to thehinge, the suspended member is attracted to an electrode uponapplication of an electrical force and restored to an original positionby a restoring force. In this manner, the array of micro-mirrors can betilted in relation to a light source. In some applications, it isbeneficial to have the hinge located beneath the micro-mirror surface ina hidden position, enabling the fill factor of the array to beincreased. As the fill factor of the micro-mirror array is increased,the potential quality of two-dimensional images created by opticalsystems using the array is improved.

As merely an example, conventional MEMS have utilized variousmicro-mirror designs to hide the hinge in a location behind the mirrorsurface. For example, torsion spring hinges attached to the backside ofthe mirror surface have been used in some designs. Unfortunately, thesetechniques also have limitations. For example, some torsion springdesigns are difficult to manufacture owing to their complex structuralfeatures. Moreover, complex mechanical structures may have reliabilityand lifetime concerns. Therefore, there is a need in the art for methodsand apparatus for a high fill factor micro-electromechanical mirrorarray with a flexible, hidden support member.

SUMMARY OF THE INVENTION

This present invention relates generally to manufacturing objects. Moreparticularly, the invention provides a method and apparatus forfabricating and operating electromechanical systems. Merely by way ofexample, the invention has been applied to a high fill factormicro-electromechanical mirror array with a hidden, flexible supportpedestal. The method and apparatus can be applied to otherelectromechanical technology as well, including actuators and sensors.

In a specific embodiment, the present invention provides anelectromechanical system. The system has a substrate (e.g., silicon)comprising a surface region. The system has a flexible member comprisinga first end coupled to the surface region of the substrate. Preferably,the flexible member comprises a second end and a length defined betweenthe first end and the second end. A base region is within a firstportion of the flexible member. The base region is defined from thefirst end to a first predetermined portion of the length of the flexiblemember. The base region is characterized by at least a firstcross-sectional area, which is parallel to the surface region of thesubstrate. The system has a tip region within a second portion of theflexible member. The tip region is defined from the second end to asecond predetermined portion of the length of the flexible member. Thetip region is characterized by at least a second cross-sectional area,which is parallel to the surface region of the substrate. A reflectivemember is coupled to the flexible member. The reflective membercomprises a reflective surface and a backside region. Preferably, thebackside region is coupled to the second end of the flexible member. Thereflective surface is substantially parallel to the surface region whilethe reflective member is in a first state and is substantiallynon-parallel to the surface region while the reflective member is in asecond state. The flexible member moves from a first positioncharacterized by the first state to a second position characterized bythe second state. The movement of the flexible member from the firstposition to the second position is constrained to lie in a first planedefined by an axis parallel to the length of the flexible member and anaxis parallel to the surface region.

In an alternative specific embodiment, the present invention provides analternative electromechanical system. The system has a first substratecomprising a surface region. A plurality of electrically activatedelectrodes is coupled to the surface region of the first substrate. Theplurality of electrically activated electrodes is coupled to anelectrical source to receive a first electrical signal. The system has aplurality of flexible members comprising a first end coupled to thesurface region of the first substrate. The members comprises a secondend and a length defined between the first end and the second end. Abase region is within a first portion of the plurality of flexiblemembers. The base region is defined from the first end to a firstpredetermined portion of the length of the flexible members. The baseregion is characterized by at least a first cross-sectional area, whichis parallel to the surface region of the substrate. A tip region iswithin a second portion of the plurality of flexible members. The tipregion is defined from the second end to a second predetermined portionof the length of the flexible members. The tip region is characterizedby at least a second cross-sectional area. A moveable structure iscoupled to the plurality of flexible members, comprising a frontsidesurface and a backside surface. The backside surface is coupled to thesecond end of the plurality of flexible members. The frontside surfaceis substantially parallel to the surface region while the moveablestructure is in a first state and is substantially non-parallel to thesurface region while the moveable structure is in a second state. Thetip region of the plurality of flexible members moves from a firstposition characterized by the first state to a second positioncharacterized by the second state upon application of a predeterminedvoltage bias associated with the first electrical signal. The movementof the tip region of the plurality of flexible members from the firstposition to the second position is constrained to lie in a planeincluding an axis parallel to the length of the plurality of flexiblemembers.

In an alternative specific embodiment, the present invention provides amethod of manufacturing an electromechanical system. The method includesdepositing a first mask layer on a first surface of a handling substrateand etching the first surface of the handling substrate to form aplurality of flexible pedestals and a plurality of walls. The methodincludes removing the first mask layer and forming a plurality ofelectrodes on an electrode substrate. The method includes aligning thehandling substrate and the electrode substrate and wafer bonding thehandling substrate to the electrode substrate by making contact betweenthe plurality of flexible pedestals and the plurality of walls. Themethod includes thinning a portion of the handling substrate by removingmaterial from a second surface of the handling substrate and depositinga second mask layer on the second surface of the handling substrate. Themethod includes etching the second surface of the handling substrate toremove at least a portion of the plurality of walls and form moveablestructures.

Many benefits are achieved by way of the present invention overconventional techniques. For example, the present technique provides aneasy to use process that relies upon conventional technology. In someembodiments, the method provides higher device yields in dies per wafer.Additionally, the method provides a process that is compatible withconventional process technology without substantial modifications toconventional equipment and processes. Preferably, the invention providesa simple structure with fewer process steps, higher yields, reliability,and other desirable features in certain embodiments. Depending upon theembodiment, one or more of these benefits may be achieved. These andother benefits will be described in more throughout the presentspecification and more particularly below.

Various additional objects, features and advantages of the presentinvention can be more fully appreciated with reference to the detaileddescription and accompanying drawings that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic side view of a micro-electromechanicalsystem with a flexible pedestal according to an embodiment of thepresent invention.

FIG. 2 is a simplified schematic side view of a micro-electromechanicalsystem with a flexible pedestal in an activated state, according to anembodiment of the present invention.

FIGS. 3A-3I illustrate a simplified schematic process flow of a methodof fabricating a micro-electromechanical system according to anembodiment of the present invention.

FIG. 3J is a simplified schematic flowchart of a method of fabricating amicro-electromechanical system according to an embodiment of the presentinvention.

FIG. 4A is a simplified schematic side view of a micro-electromechanicalsystem with a non-uniform cross-sectional area pedestal according to analternative embodiment of the present invention.

FIG. 4B is a simplified schematic top view of a micro-electromechanicalsystem with a non-uniform cross-sectional area pedestal according to analternative embodiment of the present invention.

FIG. 5 is a simplified schematic top view illustration of an alternativeembodiment of a micro-electromechanical system according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a simplified schematic side view of a micro-electromechanicalsystem with a flexible pedestal according to an embodiment of thepresent invention. A first surface 120 is provided with at least oneelectrically activated electrode 130 coupled to the first surface. Thefirst surface can be made of any suitable material. The suitablematerial generally has mechanical stability and an ability to beprocessed using semiconductor processing techniques. As merely anexample, the material can be a semiconductor. Preferably, the firstsurface is made from a single crystal silicon wafer, processed accordingto semiconductor processing techniques. In one embodiment, the firstsurface includes a plurality of control electronics and other integratedcircuits formed using semiconductor processing techniques. Othermaterials may also be used in alternative embodiments according to thepresent invention.

Electrically activated electrodes 130 and 132 are coupled to the firstsurface. The electrodes can be made of materials that conductelectricity. Merely by way of example, the electrode 130 in theembodiment illustrated in FIG. 1 is made of a metal preferentiallydeposited on the first surface. Preferably, the electrode is made of adeposited aluminum layer. In alternative embodiments according to thepresent invention, the electrode is made of titanium nitride, tungsten,or other suitable conductors.

Moveable structure 110 is suspended at a predetermined position byflexible pedestal 125, which is coupled to the first surface. In theembodiment illustrated in FIG. 1, a portion of the upper surface 115 ofthe moveable structure is a reflective surface. For example, the powerreflectance of portions of upper surface 115 may be greater than orequal to 90%. In alternative embodiments, the moveable member is coatedwith thin-film coatings to increase the power reflectance of portions ofthe upper surface. For example, multi-layer stacks of thin filmdielectric materials are utilized in a particular embodiment.

Moreover, in embodiments according to the present invention, theflexible pedestal is fabricated from a material with suitable pliabilityand reliability. The material should be elastic enough to enable themoveable member to be tilted as desired. At the same time, the materialshould have the ability to be cycled numerous times while stillmaintaining the desired reliability. In a specific embodiment, theflexible pedestal is fabricated from single crystal silicon, but this isnot required by the present invention. Additionally, the moveable memberis fabricated from single crystal silicon in a particular embodiment.Alternative embodiments according to the present invention use othermaterials that bend in response to applied forces and subsequentlyreturn to their original shape after removal of such applied forces. Forexample, some embodiments use polysilicon or metal as the material forthe flexible pedestal.

FIG. 2 is a simplified schematic side view of a micro-electromechanicalsystem with a flexible pedestal in an activated state, according to anembodiment of the present invention. As illustrated in this figure, avoltage V_(A) has been applied to the electrode 130, deflecting the leftside of the moveable structure down toward the electrode 130 andcreating a restoring torque 230 in the flexible pedestal. In oneembodiment, the position of the moveable structure illustrated in FIG. 2is referred to as an activated state. In an alternative embodiment, avoltage −V_(A) is applied to electrode 132 resulting in a repulsiveforce between the right side of the moveable structure and electrode132. Application of the voltage −V_(A) also creates a restoring torque230 in the flexible pedestal. In yet another alternative embodiment,voltages −V_(A) and V_(A) are applied to electrodes 130 and 132,respectively, resulting in a repulsive force between the left side ofthe moveable structure and electrode 130 and an attractive force betweenelectrode 132. Thus deflecting the right side of the moveable structuredown toward electrode 132 and producing the opposite tilt angle.

Embodiments according to the present invention utilize a flexiblepedestal design in which the flexible pedestal bends in a predeterminedmanner, without rotating about the longitudinal axis of the pedestal. Ingeneral, the upper end or tip 240 of the flexible pedestal is free tomove in directions that contain components in both the x-y and x-zplanes. In specific embodiments of the present invention, the motion ofthe upper end 240 of the flexible pedestal is constrained to move in asingle plane. Thus, as illustrated in FIG. 2, the flexible pedestalbends in the plane defined by the normal to the first surface 120 (they-axis) and the axis lying in the plane of the paper that isperpendicular to the normal (the x-axis), namely, the x-y plane.Consequently, the torque 230 is orthogonal to the x-y plane. In theembodiment illustrated in FIG. 2, there is no motion of the tip of theflexible pedestal in the x-z plane and no rotational motion around thez-axis, resulting in the bending motion of the flexible pedestal beingconstrained to lie in only the x-y plane.

As illustrated in FIG. 2, the left side of the moveable structure makescontact with the first surface 120. However, this is not required by thepresent invention. An example of one way of utilizing landing pads andlanding posts to reduce the amount and impact of contact between themoveable structure and the first surface is described in U.S. patentapplication Ser. No. 10/718,482, filed Nov. 19, 2003, commonly owned,and hereby incorporated by reference for all purposes. Moreover, inalternative embodiments, the electrodes may be elevated above the firstsurface, reducing the distance between the electrodes and the moveablesurface, and thereby increasing the electrostatic forces resulting fromthe application of voltages to the electrodes.

In embodiments according to the present invention, the height andposition of the flexible pedestal are selected so that the upper surfaceof the moveable structure is tilted at a predetermined angle withrespect to the horizontal when the moveable structure is in theactivated state. In embodiments according to the present invention inwhich the upper surface of the moveable structure comprises reflectiveportions, an incident ray of light will be reflected at predeterminedangles depending on the tilt angle of the moveable structure when in theactivated position. In the embodiment illustrated in FIG. 2, thedimensions of the moveable structure and the height and position of theflexible pedestal are selected so that the moveable structure is tiltedat an angle of 12° with respect to the horizontal when in the activatedstate. Alternative embodiments have either increased or decreased tiltangles with respect to the horizontal.

Moreover, in embodiments according to the present invention, thelongitudinal length of the moveable structure is a predetermined length.In the embodiment illustrated in FIG. 2, the longitudinal length 220 is15 μm. Alternatively, the length ranges from a few microns to severalhundred microns in other embodiments. Of course, the longitudinal lengthof the moveable structure will depend on the particular applications. Inthe embodiment according to the present invention illustrated in FIG. 2,the electrode 130 is complemented by electrode 132 located on theopposite side of the flexible pedestal. These complementary electrodesare used in one embodiment to alternately attract or repel the moveablestructure, producing tilting to the left or to the right. In alternativeembodiments, a single electrode or more than two electrodes areutilized.

FIGS. 3A-3J and FIG. 3K illustrate a simplified schematic process flowand flowchart, respectively, of a method of fabricating amicro-electromechanical system according to an embodiment of the presentinvention. As illustrated in the figures, the process employs twosubstrates which are processed separately, subsequently bonded togetherto form a composite structure, and processed further as a compositestructure. In alternative embodiments, the micro-electromechanicalsystem is fabricated by sequentially depositing and processing layers ona single substrate. In FIGS. 3A-3J, the figures as drawn are truncatedon the left and rights sides of the figures for purposes of clarity.

FIG. 3A illustrates a handling substrate 304 with an insulating layer306 and device layer 308. The handling substrate is fabricated from asuitable material. In one embodiment, the handling substrate is a singlecrystal silicon wafer, but this is not required by the presentinvention. The insulating layer 306 is a silicon oxide layer in anembodiment according to the present invention. In alternativeembodiments, the insulating layer comprises a silicon nitride layer or acomposite oxide/nitride layer. In step 380 of FIG. 3K, a mask layer 310is deposited on top of device layer 308 as illustrated in FIG. 3B. Inone embodiment according to the present invention, silicon oxide isdeposited and patterned to form the mask layer. Standardphotolithography techniques can be used to generate the mask layer. Themask layer is typically characterized by a two-dimensional pattern inthe plane of the handling substrate. The mask layer defines regions ofthe device layer that will be etched during a subsequent etching processor series of etching processes, forming cavities or recessed regions 312in the device layer along with flexible pedestals 125 and walls 316.

In step 382, the device layer is etched to form the flexible pedestals125 and the walls 316 in an upper portion of the device layer 308. Inalternative embodiments, the flexible pedestals and the walls are formedin subsequent etching processes, thereby optimizing the shape of thepedestals and the shape of the walls independently. Additional maskingsteps are utilized as needed for each of the additional etchingprocesses. The etch processes utilized, as discussed below, will formflexible pedestals and walls with predetermined profiles and heights.

In one embodiment, the substrate is etched in a reactive ion etchchamber flowing with SF₆, HBr, and oxygen gases at flow rates of 100sccm, 50 sccm, and 10 sccm respectively. The operating pressure is inthe range of 10 to 50 mTorr, the bias power is 60 W, and the sourcepower is 300 W. In another embodiment, the substrate is etched in areactive ion etch chamber flowing with Cl₂, HBr, and oxygen gases atflow rates of 100 sccm, 50 sccm, and 10 sccm, respectively. In theseembodiments, the etch processes stop when the cavities are about 3-4microns deep. This depth is measured using in-situ etch depthmonitoring, such as in-situ optical interferometer techniques, or bytiming the etch rate.

In another embodiment, the cavities are formed in the substrate by ananisotropic reactive ion etch process. The substrate is placed in areaction chamber. SF₆, HBr, and oxygen gases are introduced into thereaction chamber at a total flow rate of 100 sccm, 50 sccm, and 20 sccm,respectively. A bias power setting of 50 W and a source power of 150 Ware used at a pressure of 50 mTorr for approximately 5 minutes. Thesubstrate is then cooled with a backside helium gas flow of 20 sccm at apressure of 1 mTorr. In one particular embodiment, the etch processesstop when the cavities are about 3-4 microns deep. This depth ismeasured using in-situ etch depth monitoring, such as in-situ opticalinterferometer techniques, or by timing the etch rate. The mask layer isremoved in step 384.

FIG. 3D illustrates a simplified cross-sectional view of an electrodesubstrate according to an embodiment of the present invention. Substrate320 is processed according to well-known semiconductor processingtechniques to form electrodes 130 and 132 and control electronics (notshown) on the surface of substrate 320. Substrate 320 is a transparentmaterial in one embodiment of the present invention. Merely by way ofexample, in one embodiment, the substrate is quartz and the electrodesand control transistors are fabricated from polysilicon, oxides, andmetals. In additional embodiments, an array of memory cells, row addresscircuitry, and column data loading circuitry are formed on the electrodesubstrate. The methods of forming this electrical circuitry are wellknow in the art. For example, DRAM, SRAM, and latch devices are commonlyknown and may perform addressing functions. A passivation layer such assilicon oxide or silicon nitride is deposited over the controltransistors in one embodiment according to the present invention,selectively separating the control transistors from metallizedelectrodes.

In embodiments according to the present invention in which the spacingbetween flexible pedestals and the walls is relatively large onsemiconductor scales (for example, a spacing of 15 μm), complexelectrical circuitry can be manufactured on the surface of the electrodesubstrate in the regions between the flexible pedestals. Possiblecircuitry includes, but is not limited to, storage buffers to store timesequential pixel information, circuitry to compensate for possiblenon-uniformity of the handling and electrode substrates or theirdeposited layers, and circuitry to form pulse width modulationconversions.

In step 388, the handling substrate and the electrode substrate arebonded together as illustrated in FIG. 3E. In FIG. 3E, the handlingsubstrate has been inverted and bonded to the top of the electrodesubstrate. As illustrated in FIG. 3E, the substrates have been alignedso that the flexible pedestals 125 are positioned an equal distancebetween electrodes 130 and 132. Additionally, the walls 316 arepositioned an equal distance between electrodes 132 and 130. In oneembodiment, the substrates are optically aligned using double focusingmicroscopes. In this embodiment, alignment marks located on bothsubstrates are utilized to position the substrates during the alignmentprocess. In another embodiment, the substrates are bonded together usinglow temperature bonding methods such as anodic or eutectic bonding. Inalternative embodiments, other bonding methods are employed, forexample, the use of thermoplastics or dielectric spin glass bondingmaterials. After bonding, the handling substrate is bonded to theelectrode substrate at the locations where the flexible pedestals andthe walls make contact with the electrode substrate.

In step 390, illustrated in FIG. 3F, the handling substrate is removedusing a thinning process. For example, in one embodiment, the handlingsubstrate is removed in a lapping apparatus that employs mechanicalpolishing and grinding to remove layer 304. In step 392, insulatinglayer 306 is removed as illustrated in FIG. 3G. Merely by way ofexample, the insulating layer is removed in one embodiment by chemicaletching. In alternative embodiment, the insulating layer is removed bymechanical grinding or polishing.

Subsequent to the removal of the oxide layer, in a particular embodimentaccording to the present invention, the device layer 308 is polished. Inalternative embodiments, the device layer is thinned to a predeterminedthickness and subsequently polished, however this is not required by thepresent invention. In yet another alternative embodiment, the thicknessof the device layer 308 is selected during the initial fabrication ofhandling substrate 304 and is maintained at this pre-selected thicknessduring subsequent processing. In this alternative embodiment, thesurface morphology of layer 308/layer 306 interface is controlled duringthe initial fabrication of the handling substrate and no thinning orpolishing steps are needed. As will be apparent in FIG. 31, thethickness of the device layer 308 will impact the thickness of the upperportion of the moveable structure. In an embodiment in which themoveable structure functions as a micro-mirror, the thickness of themirror is dependent on the thickness of device layer 308.

In step 394 a reflective surface 320 is formed at the top surface oflayer 308. As illustrated in FIG. 3H, a reflective layer is deposited ontop of layer 308, but this is not required by the present invention. Inone embodiment, the layer 308 is polished to create a reflectivesurface. In an alternative embodiment, at least one layer of reflectivematerial is deposited on top of layer 308. Merely by way of example, thereflective material can be a metallic reflective layer, such asaluminum. In the embodiment with an aluminum reflective layer, the layer308 is first coated with approximately 10 nm of a titanium seed thinfilm. An aluminum layer approximately 30 nm thick is then deposited onthe titanium seed layer. In this embodiment, a reflectance of over 90%is achieved over a significant portion of the visible spectrum. Inalternative embodiments, multi-layer dielectric stacks are utilized toform reflective surface 320. The multi-layer dielectric stacks in oneembodiment are designed to provide a reflectance of over 99% over asignificant portion of the visible spectrum. Alternatively, thereflectance ranges from about 80% to about 99.1% in other embodiments.Of course, the reflectance value will depend on the particularapplications.

In step 396, the moveable structures 332 are separated from adjacentstructures by an etching process as illustrated in FIG. 31. Typically, amask layer (not shown) is deposited to top of the reflective surface 320and used during an etching process that removes portions of layer 320,308, and the walls 316 in areas 330, illustrated by a dashed line inFIG. 31. After the etching process is completed, the mask layer (notshown) is removed and the structure illustrated in FIG. 3J is produced.Adjacent moveable structures 332 are supported by flexible pedestals 125and are located above corresponding electrodes 130 and 132.

The dimensions of the flexible pedestal will impact its elasticity andthe force required to modulate the position of the moveable structure.For many materials used to fabricate the flexible pedestal, a smallercross-sectional area will result in increased flexibility. At the sametime, a decrease in the cross-sectional area of the pedestal's base willincrease the difficulty of reliably bonding the base of the flexiblepedestal to the first surface, as described above. Thus, there is, insome embodiments, a tradeoff between pedestal flexibility and ease ofmanufacturing. FIGS. 4A and 4B are simplified schematic side and topviews, respectively, of a MEMS with a flexible pedestal characterized bya non-uniform cross-sectional area according to an alternativeembodiment of the present invention. Moreover, in some embodiments, atradeoff also exists between the ease of bonding the walls to theelectrode substrate and increasing the fill factor of the array ofmoveable structures. As the width of the walls, which provide structuralsupport during fabrication, decrease, possible manufacturingdifficulties during the bonding process increase. Counterbalancing thiseffect, as the wall width increases, the fill factor of the moveablestructures after the walls are removed, is decreased. In embodiments ofthe present invention, the wall width is a predetermined value. In aparticular embodiment, the wall width is 0.6 μm and uniform throughoutthe handling substrate. Alternatively, the width ranges from about 0.2μm to about 1 μm in other embodiments. Of course, the width will dependupon the particular applications.

FIG. 4B is a simplified schematic top view of a MEMS with a non-uniformcross+ sectional area pedestal according to an alternative embodiment ofthe present invention. The perimeter of the reflective surface 115 ofthe moveable member 110 is illustrated as rectangle 415 in this figure.Electrodes 130 and 132, not visible from the top, but illustrated forpurposes of clarity, are illustrated as triangular areas 430 and 432.The base region of the flexible pedestal, coupled to the first surfaceat location 410 in FIG. 4A, is illustrated as dashed rectangle 447 inFIG. 4B. The base or first end of the pedestal 410 is characterized byat least a first cross-sectional area defined by a first width(dimension 452 in FIG. 4B) and a first length (dimension 440 in FIG.4B). As illustrated in FIG. 4B, the first width is less than the firstlength.

The top region or tip of the flexible pedestal, coupled to the lowersurface of moveable structure 110 at location 420 in FIG. 4A, isillustrated as solid rectangle 445 in FIG. 4B. Thus, the dimensions ofthe pedestal at its tip or second end is width 450 and length 440. Thesecond end of the pedestal 420 is characterized by at least a secondcross-sectional area defined by a second width (dimension 450 in FIG.4B) and a second length (dimension 440 in FIG. 4B). As illustrated inFIG. 4B, the second width is less than the second length. Moreover, thecross-sectional area 447 of the base or first region of the flexiblepedestal is greater than cross-sectional area 445 of the tip or secondregion of the flexible pedestal. The distance from the first end of thepedestal to the second end defines a length of the pedestal. In FIG. 4B,this length lies along the longitudinal axis of the pedestal, parallelto the x-axis.

The cross-sectional profile illustrated in FIG. 4A can be manufacturedutilizing various semiconductor etch processes well known to one ofskill in the art. For example, an isotropic etch is utilized in aspecific embodiment to create the cross-sectional profile illustrated inFIG. 4A.

Moreover, as illustrated in FIGS. 4A and 4B the cross-sectional shape ofthe flexible pedestal is rectangular with the cross-sectional areavarying as a function of the pedestal length. However, in otherembodiments according to the present invention, the flexible pedestal ischaracterized by different cross-sectional shapes. For example, flexiblepedestals in the shape of a circle, oval, diamond, and other geometricshapes are utilized in alternative embodiments. Of course, the degreesof freedom associated with the bending motion of the flexible pedestalwill depend on the particular cross-sectional shape. For example, asillustrated in FIGS. 4A and 4B, the pedestal will be constrained to bendin a predetermined manner. As illustrated, the first end of the pedestalis substantially fixed, as it is bonded to the first surface. However,the second end of the pedestal is capable of moving in the plane definedby the longitudinal axis of the pedestal and the width of the pedestal(the x-y plane). The rigidity produced by the length 440 of the pedestalin comparison with the width, and the placement of the electrodes alonga line parallel to the width of the pedestal and passing through thecenter of the pedestal, result in the tip of the pedestal only moving inthe x-y plane, resulting in the pedestal only bending in the x-y plane.A rotational torque orthogonal to the x-y plane (about the z-axis) willthus be present in the flexible pedestal when it is positioned in thesecond or activated position. As described, the tip of the pedestal issubstantially fixed in the x-z plane due to the pedestal shape andelectrode placement. Moreover, the pedestal does not experience anyrotational bending around its longitudinal axis (x-axis) when positionedin the second position.

In embodiments in which the cross-sectional shape of the pedestal is anellipse, the bending motion will occur in the plane defined by thelongitudinal axis of the pedestal and the minor axis of the ellipse,rotating about the axis parallel to the major axis of the ellipse.Embodiments in which the cross-sectional shape of the pedestal is acombination of such geometrical shapes, and the resulting constraints onthe bending motion, will be apparent to those of skill in the art.

FIG. 4B is a simplified schematic top view of a MEMS with a non-uniformcross-sectional area pedestal according to an alternative embodiment ofthe present invention. The perimeter of the reflective surface 115 ofthe moveable member 110 is illustrated as rectangle 415 in this figure.Electrodes 130 and 132, not visible from the top, but illustrated forpurposes of clarity, are illustrated as triangular areas 430 and 432.The base of the flexible pedestal, coupled to the first surface atlocation 410 in FIG. 4A, is illustrated as dashed rectangle 447 in FIG.4B. The dimensions of the pedestal at its base is width 452 and length440. The top of the flexible pedestal, coupled to the moveable structureat location 420 in FIG. 4A, is illustrated as solid rectangle 445 inFIG. 4B. Thus, the dimensions of the pedestal at its top is width 450and length 440. As illustrated, the cross-sectional area 447 is greaterthan cross-sectional area 445.

The flexible pedestal illustrated in FIGS. 4A and 4B provides anembodiment according to the present invention in which the elasticity ofthe pedestal is increased by the narrowing of the cross-section as afunction of height while still maintaining the width of the pedestal'sbase at location 410, thereby reducing possible manufacturingdifficulties. Although the embodiment illustrated in FIG. 4A utilizes aflexible pedestal in which the cross-sectional are decreasesmonotonically from the base to the top, this is not required by thepresent invention. Alternative embodiments utilize flexible pedestals ofnon-uniform cross-section in which the cross-sectional area varies inother continuous and discontinuous manners.

In embodiments according to the present invention, the length 440 of theflexible pedestal is a predetermined distance. In a specific embodiment,the length of the flexible pedestal is 3 μm and uniform along the lengthof the pedestal. In other embodiments, the length varies along thelength of the pedestal. As discussed above, for many materials, thedimensions of the pedestal, including the length, impact the flexibilityof the pedestal. For example, in some embodiments, as the length of thepedestal increases, the flexibility typically decreases. Increases inpedestal length are balanced against decreases in width in someembodiments to maintain the flexibility at a desired value. In designingthe pedestal dimensions, including the width and length, the designercan utilize these design parameters to optimize the system performance.In one embodiment, the flexible pedestal runs continuously from onecorner of the moveable structure to the opposite corner. As illustratedin FIG. 4B, the length 440 of the pedestal in this embodiment would be√{square root over (2)} times the length of a side of the moveablestructure 415.

As illustrated in FIGS. 4A and 4B, moveable structures 110 are laid outin the pattern of a two-dimensional array. In a specific embodiment, themoveable structures form a two-dimensional micro-mirror array. Asdescribed with relation to FIG. 3E, the walls 316, which form acontinuous two dimensional array of rows and columns in areas 422 asillustrated in FIG. 4B, and the pedestals 125 are bonded to the firstsurface 120 during the bonding process. After the two substrates arebonded together, the walls 316 are removed, separating adjacentmicro-mirrors from each other by spaces 422. As illustrated by thedashed lines in FIG. 4A, the entire wall 316 is removed during thisprocess, leaving gaps 422 between adjacent mirrors. After removal of thewalls, the flexible pedestals 125 support the moveable structures 110.

In embodiments according to the present invention, the dimensions of theflexible pedestal are selected to achieve particular system goals. Forexample, in one embodiment, the length and width of the flexiblepedestal are predetermined. As will be evident to one of skill in theart, the elasticity of the flexible pedestal will typically be afunction of the pedestal dimensions. For example, as the length andwidth of the pedestal increases, the elasticity of the pedestaltypically decreases. In a specific embodiment, the length of thepedestal is 3 μm and the width of the pedestal is 0.2 μm. In thisspecific embodiment, the length and width of the pedestal is uniform asa function of height. In the embodiment illustrated in FIGS. 4A and 4B,the length of the pedestal is 0.2 μm and uniform as a function ofheight. However, as illustrated in FIGS. 4A and 4B, the width of thepedestal is non-uniform as a function of height. As illustrated in FIGS.4A and 4B, the width of the pedestal is 0.3 μm at the base (dimension452) and 0.1 μm at the top (dimension 450).

In another specific embodiment, the length of the pedestal is increasedto improve the reliability of the bond between the base of the pedestaland the first surface. In an alternative specific embodiment, the widthof the base of the pedestal is increased to improve the reliability ofthe bond between the base of the pedestal and the first surface. In yetanother alternative embodiment, the length and average width of thepedestal are increased to improve the reliability of the bond betweenthe base of the pedestal and the first surface.

FIG. 5 is a simplified schematic top view illustration of an alternativeembodiment according to the present invention. FIG. 5 illustrates themicro-electromechanical array of this embodiment after the bonding andwall removal process is completed as described in relation to FIG. 4A Asshown in FIG. 5, two flexible pedestals 510 and 512 support each cornerof each moveable structure 110.

In embodiments according to the present invention, the dimensions of theflexible pedestals are selected to achieve particular system goals. Forexample, in one embodiment, the lengths and widths of the flexiblepedestals are predetermined. As illustrated in FIG. 5, a first pedestal510 is coupled to a first corner of the moveable structure 110 and asecond flexible pedestal 512 is coupled to a second corner of themoveable structure. In the embodiment illustrated in FIG. 5, the firstcorner and the second corner are opposite each other. The pedestals 510and 512 have a non-uniform cross-section as a function of height. Thewidth at the base 522 (represented by a dashed line) is larger than thewidth at the top 520 (represented by a solid line). For example, in theembodiment illustrated in FIG. 5, pedestals 510 and 512 have a length(dimension 534) of 2 μm, a base width (dimension 530) of 0.3 μm, and atop width (dimension 532) of 0.1 μm. In alternative embodiments, thecross-sectional area of the flexible pedestal does not monotonicallydecrease as a function of the distance from the first surface (heightmeasured from the base to the top). Alternative embodiments utilizeflexible pedestals of non-uniform cross-section in which thecross-sectional area varies in other continuous and discontinuousmanners.

In the embodiment illustrated in FIG. 5, the two pedestals supportingthe moveable structure are equal in dimensions, resulting in a symmetricstructure. However, this is not required by the present invention.Alternative embodiments according to the present invention utilizepedestals of varying length and width. Moreover, in yet otheralternative embodiments, the number of pedestals per moveable structureis greater than two. For example, one specific embodiment utilizes threepedestals, with two pedestals located at the first and second (opposite)corners of the moveable structure and the third located near the centerof the moveable structure. Additional embodiments utilize additionalpedestals to support the moveable structure depending on the particularapplications.

As discussed in relation to FIGS. 4A and 4B, the geometry of thecross-sectional area of the pedestal and the placement of the electrodeswill constrain the motion of the tips of the flexible pedestals to movein the x-y plane. Therefore, the motion of the moveable structure willbe constrained to lie in the x-y plane. No rotational torques about thelongitudinal axes of the flexible pedestals (lying parallel to thex-axis) are generated in the embodiment illustrated in FIG. 5 as therestoring torques present in the flexible pedestals are orthogonal tothe x-y plane.

The examples and embodiments described herein are for illustrativepurposes only. Various modifications or changes in light thereof will besuggested to persons skilled in the art and are to be included withinthe spirit and purview of this application and scope of the appendedclaims. It is not intended that the invention be limited, except asindicated by the appended claims.

1. An electromechanical system, comprising: a substrate comprising asurface region; a flexible member comprising a first end coupled to thesurface region of the substrate, the flexible member comprising a secondend and a length defined between the first end and the second end; abase region within a first portion of the flexible member, the baseregion being defined from the first end to a first predetermined portionof the length of the flexible member, the base region beingcharacterized by at least a first cross-sectional area, the firstcross-sectional area being parallel to the surface region of thesubstrate; a tip region within a second portion of the flexible member,the tip region being defined from the second end to a secondpredetermined portion of the length of the flexible member, the tipregion being characterized by at least a second cross-sectional area,the second cross-sectional area being parallel to the surface region ofthe substrate; and a reflective member coupled to the flexible member,the reflective member comprising a reflective surface and a backsideregion, the backside region being coupled to the second end of theflexible member, the reflective surface being substantially parallel tothe surface region while the reflective member is in a first state andbeing substantially non-parallel to the surface region while thereflective member is in a second state; whereupon the flexible membermoves from a first position characterized by the first state to a secondposition characterized by the second state, the movement of the flexiblemember from the first position to the second position being constrainedto lie in a first plane defined by an axis parallel to the length of theflexible member and an axis parallel to the surface region wherein anangle between the reflective member in the first state and thereflective member in the second state, measured in the first plane, is12°.
 2. The electromechanical system of claim 1 wherein a portion of thereflective member has a reflectance greater than 95%.
 3. Theelectromechanical system of claim 2 wherein the reflective membercomprises a micro-mirror forming a portion of a micro-mirror array. 4.The electromechanical system of claim 1 wherein the flexible member andthe reflective member are fabricated from single crystal silicon.
 5. Theelectromechanical system of claim 1 wherein the movement of the flexiblemember from the first position to the second position is constrained tolie in the first plane because a first dimension of the flexible memberparallel to the axis parallel to the surface region is less than asecond dimension of the flexible member orthogonal to the axis parallelto the length of the flexible member and the axis parallel to thesurface region.
 6. The electromechanical system of claim 5 wherein thefirst dimension is a cross-sectional width of the flexible member andthe second dimension is a cross-sectional length of the flexible member,the product of the cross-sectional width and the cross-sectional lengthbeing the first cross-sectional area.
 7. The electromechanical system ofclaim 6 wherein the cross-sectional length of the flexible memberprevents movement of the flexible member in any plane other than thefirst plane.
 8. The electromechanical system of claim 6 wherein themovement of the flexible member from the first position to the secondposition results in a restoring torque purely orthogonal to the firstplane.
 9. (canceled)
 10. The electromechanical system of claim 1 whereinthe second cross-sectional area is smaller than the firstcross-sectional area.
 11. An electromechanical system, comprising: afirst substrate comprising a surface region; a plurality of electricallyactivated electrodes coupled to the surface region of the firstsubstrate, the plurality of electrically activated electrodes beingcoupled to an electrical source to receive a first electrical signal; aplurality of flexible members comprising a first end coupled to thesurface region of the first substrate, the members comprising a secondend and a length defined between the first end and the second end; abase region within a first portion of the plurality of flexible members,the base region being defined from the first end to a firstpredetermined portion of the length of the flexible members, the baseregion being characterized by at least a first cross-sectional area, thefirst cross-sectional area being parallel to the surface region of thesubstrate; a tip region within a second portion of the plurality offlexible members, the tip region being defined from the second end to asecond predetermined portion of the length of the flexible members, thetip region being characterized by at least a second cross-sectionalarea; and a moveable structure, coupled to the plurality of flexiblemembers, comprising a frontside surface and a backside surface, thebackside surface being coupled to the second end of the plurality offlexible members, the frontside surface being substantially parallel tothe surface region while the moveable structure is in a first state andbeing substantially non-parallel to the surface region while themoveable structure is in a second state; whereupon the tip region of theplurality of flexible members moves from a first position characterizedby the first state to a second position characterized by the secondstate upon application of a predetermined voltage bias associated withthe first electrical signal, the movement of the tip region of theplurality of flexible members from the first position to the secondposition being constrained to lie in a plane including an axis parallelto the length of the plurality of flexible members, wherein the moveablestructure tilts at an angle of 12° with respect to the first surfaceupon application of the predetermined voltage bias associated with thefirst electrical signal.
 12. The electromechanical system of claim 111wherein the plurality of flexible members comprise a first flexiblemember coupled to a first corner of the moveable structure and a secondflexible member coupled to a second corner of the moveable structure,the second corner located opposite the first corner.
 13. Theelectromechanical system of claim 12 wherein the movement of the tipregion of the plurality of flexible members from the first position tothe second position is constrained to lie in the plane including theaxis parallel to the length of the plurality of flexible members becausea dimension of the plurality of flexible members parallel to a linerunning from the first corner of the moveable structure to the secondcorner of the moveable structure is greater than a dimension of theplurality of flexible members orthogonal to the line and parallel to thesurface region.
 14. The electromechanical system of claim 12 wherein aportion of the frontside surface of the moveable structure is adapted toreflect incident radiation.
 15. The electromechanical system of claim 14wherein the portion of the frontside surface of the moveable structurehas a reflectance greater than 95%.
 16. The electromechanical system ofclaim 15 wherein the moveable structure comprises an element of an arrayof micro-mirrors.
 17. The electromechanical system of claim 11 whereinthe plurality of flexible members and the moveable structure arefabricated from single crystal silicon.
 18. (canceled)
 19. Theelectromechanical system of claim 11 wherein the second cross-sectionalarea is smaller than the first cross-sectional area.
 20. A method ofmanufacturing an electromechanical system, the method, comprising:depositing a first mask layer on a first surface of a handlingsubstrate; etching the first surface of the handling substrate to form aplurality of flexible pedestals and a plurality of walls; removing thefirst mask layer; forming a plurality of electrodes on an electrodesubstrate; aligning the handling substrate and the electrode substrate;wafer bonding the handling substrate to the electrode substrate bymaking contact between the plurality of flexible pedestals and theplurality of walls; thinning a portion of the handling substrate byremoving material from a second surface of the handling substrate;depositing a second mask layer on the second surface of the handlingsubstrate; and etching the second surface of the handling substrate toremove at least a portion of the plurality of walls and form moveablestructures.
 21. The method of claim 20 further comprising polishing thesecond surface of the handling substrate.
 22. The method of claim 20further comprising depositing at least one reflective layer on thesecond surface of the handling substrate.
 23. The method of claim 22wherein the reflective layer is characterized by a reflectance value ofgreater than 90%.
 24. The method of claim 20 wherein the flexiblepedestals provide mechanical support for the moveable structures.